Imaging lens

ABSTRACT

An imaging lens includes a first lens having positive refractive power; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; and a seventh lens, arranged in this order from an object side to an image plane side. The first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are arranged respectively with a space in between. The fifth lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius. The seventh lens is formed in a shape so that a surface thereof on the image plane side and a surface thereof on the object side are aspheric.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of a prior application Ser. No.15/657,303, filed on Jul. 24, 2017, allowed, which a prior applicationSer. No. 14/837,123, issued on Aug. 29, 2017 as U.S. Pat. No. 9,746,641,which is a continuation application of a prior application Ser. No.14/451,491, issued on Sep. 29, 2015 as U.S. Pat. No. 9,146,380.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image ofan object on an imaging element such as a CCD sensor and a CMOS sensor.In particular, the present invention relates to an imaging lens suitablefor mounting in a relatively small camera such as a camera to be builtin a portable device including a cellular phone and a portableinformation terminal, a digital still camera, a security camera, avehicle onboard camera, and a network camera.

In recent years, in place of cellular phones that are intended mainlyfor making phone calls, so-called “smartphones” have been more widelyused, i.e., cellular phones with functions of portable informationterminals (PDA) and/or personal computers. Since the smartphonesgenerally are highly functional as opposed to the cellular phones, it ispossible to use images taken by a camera thereof in variousapplications.

Generally speaking, product groups of cellular phones and smartphonesare often composed of products of various specifications, from productsfor beginner users to products for advanced users. Among them, animaging lens for mounting in products for advanced users requires a lensconfiguration of high resolution, which can be applied also in highpixel count imaging elements.

As one of methods to achieve an imaging lens of high resolution, thereis a method of increasing the number of lenses that compose the imaginglens. However, an increase in the number of lenses easily causes anincrease in size of the imaging lens, so that such an approach is notfavorable for mounting in the above-described small-sized cameras suchas cellular phones and smartphones. For this reason, the imaging lenseshave been developed while restraining an increase in the number oflenses as much as possible. However, with rapid technology advancementin increasing the pixel count of an imaging element in these days, itbecame more interesting to develop an imaging lens that can achieve highresolution rather than a short total track length of the imaging lens.For example, according to a camera unit that became newly available, itis possible to obtain quality images equivalent to those obtained bydigital still cameras by attaching a camera unit having an imaging lensand an imaging element to cellular phones, smartphones, or the like,instead of mounting it in a cellular phone, smartphone, or the like asis conventional.

A lens configuration having seven lenses is slightly disadvantageous fordownsizing of an imaging lens due to the large number of lenses thatcompose the imaging lens. However, since such lens configuration hasflexibility in designs, it has potential to achieve satisfactorycorrection of aberrations and downsizing of the imaging lens in abalanced manner. As such imaging lens having a seven-lens configuration,there is known, for example, the one described in Patent Reference.

Patent Reference: Japanese Patent Application Publication No.2012-155223

The imaging lens described in Patent Reference includes a first lenshaving a biconvex shape, a second lens that has a biconcave shape and isjoined to the first lens, a third lens that is negative and has a shapeof a meniscus lens directing a convex surface thereof to an object side,a fourth lens that is positive and has a shape of a meniscus lensdirecting a concave surface thereof to the object side, a fifth lensthat is negative and has a shape of meniscus lens directing a convexsurface thereof to the object side, a sixth lens having a biconvexshape, and a seventh lens having a biconcave shape, arranged in theorder from the object side.

According to the imaging lens disclosed in Patent Reference, throughrestraining the ratio between a focal length of a first lens groupcomposed of lenses from the first lens to the fourth lens and a focallength of a second lens group composed of the lenses from the fifth lensto the seventh lens within certain range, it is possible to achievedownsizing of the imaging lens and satisfactory correction ofaberrations.

According to the imaging lens described in Patent Reference, the size ofthe imaging lens is small, but correction of an image surface isinsufficient. Especially distortion is relatively large, there is alimit by itself in achieving a high resolution imaging lens. Accordingto the lens configuration described in Patent Reference, it is difficultto achieve satisfactory aberration correction while downsizing theimaging lens.

Here, such difficulty is not a problem specific to the imaging lens tobe mounted in cellular phones and smartphones. Rather, it is common evenfor an imaging lens to be mounted in a relatively small camera such asdigital still cameras, portable information terminals, security cameras,onboard cameras, and network cameras.

In view of the above-described problems in the conventional techniques,an object of the present invention is to provide an imaging lens thatcan attain both downsizing and satisfactory correction of aberrations.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to a firstaspect of the present invention, an imaging lens includes a first lensgroup having positive refractive power, a second lens group havingnegative refractive power, and a third lens group having negativerefractive power, arranged in the order from the object side to theimage plane side. The first lens group includes a first lens havingpositive refractive power, a second lens having negative refractivepower, and a third lens having positive refractive power. The secondlens group includes a fourth lens and a fifth lens. The third lens groupincludes a sixth lens and a seventh lens. Among them, the fourth lenshas an object-side surface having negative curvature radius. The fifthlens has an image plane-side surface having positive curvature radius.In addition, when the first lens has an Abbe's number νd1, the secondlens has an Abbe's number νd2, and the third lens has an Abbe's numberνd3, the imaging lens of the invention satisfies the followingconditional expressions (1) to (3):

40<νd1<75  (1)

20<νd2<35  (2)

40<νd3<75  (3)

According to the invention, the imaging lens includes the three lensgroups from the first lens group to the third lens group, and refractivepowers of the lens groups are arranged in the order of positive,negative, and negative from the object side. Among them, the refractivepowers of the first lens group and the second lens group are arranged inthe order of positive and negative, so that a chromatic aberration issatisfactorily corrected in those lens groups.

Therefore, according to the imaging lens of the invention, it ispossible to satisfactorily correct aberrations, especially the chromaticaberration, and also possible to obtain satisfactory image-formingperformance necessary for a high-resolution imaging lens. In addition,according to the imaging lens of the invention, the third lens group hasnegative refractive power, so that it is possible to suitably reduce thesize of the imaging lens.

The first lens group includes the three lenses, in which refractivepowers are arranged in the order of positive, negative, and positive.Those three lenses are respectively formed from materials that satisfythe conditional expressions (1) through (3). With the arrangement ofrefractive powers and arrangement of the Abbe's numbers of those lenses,in the first lens group, it is possible to suitably restrain generationof a chromatic aberration, and also possible to satisfactorily correctthe chromatic aberration if generated any. Moreover, in the second lensgroup, the fourth lens arranged on the object side has an object-sidesurface having negative curvature radius, and the fifth lens arranged onthe image plane side has an image plane-side surface having positivecurvature radius, so that it is possible to suitably correct a fieldcurvature. Therefore, according to the imaging lens of the invention, itis possible to obtain satisfactory image-forming performance.

According to a second aspect of the invention, when the fourth lens haspositive refractive power, the fifth lens has negative refractive power,the fourth lens has an Abbe's number νd4, and the fifth lens has anAbbe's number νd5, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expressions(4) and (5):

20<νd4<35  (4)

20<νd5<35  (5)

According to the imaging lens of the invention, the second lens group iscomposed of two lenses having positive refractive power and negativerefractive power, so that it is possible to more satisfactorily correctaberrations, especially chromatic aberration, generated in the firstlens group. Generally speaking, in order to obtain a high-resolutionimaging lens, it is necessary to satisfactorily correct aberrations,especially the chromatic aberration. According to the imaging lens ofthe invention, with the arrangement of refractive powers of therespective lens groups from the first lens group to the third lensgroup, the arrangement of refractive powers and the order of Abbe'snumbers of the three lenses that compose the first lens group, and thearrangement of the refractive powers and order of the Abbe's numbers ofthe two lenses that compose the second lens group, it is possible tomore satisfactorily correct the chromatic aberration than conventionalimaging lenses.

According to the imaging lens having the above-described configuration,the sixth lens and the seventh lens are preferably formed so as to haveboth negative refractive powers near the optical axis, and have shapeshaving stronger positive refractive powers as it goes to the lensperipheries.

The third lens group includes two lenses having negative refractivepowers. Those two lenses have both negative refractive powers near theoptical axis and have shapes having stronger positive refractive powersas it goes to the lens peripheries. For this reason, it is possible tosatisfactorily correct not only an axial chromatic aberration, but alsoan off-axis chromatic aberration of magnification. In addition, as iswell known, an imaging element such as a CCD sensor or CMOS sensor has aso-called chief ray angle (CRA) set in advance, i.e. range of anincident angle of a light beam that can be taken in the sensor. With theabove-described lens shapes of the sixth lens and the seventh lens, itis possible to suitably restrain incident angles of light beams emittedfrom the imaging lens to the image plane within the range of CRA. Assuch, it is possible to suitably restrain generation of shading, aphenomenon of obtaining an image that is dark at the periphery.

Furthermore, according to a third aspect of the invention, when thesixth lens has an Abbe's number νd6 and the seventh lens has an Abbe'snumber νd7, the imaging lens having the above-described configurationpreferably further satisfies the following conditional expressions (6)and (7):

40<νd6<75  (6)

40<νd7<75  (7)

According to a fourth aspect of the invention, when the whole lenssystem has a focal length f and a distance on an optical axis betweenthe third lens and the fourth lens is D34, the imaging lens having theabove-described configuration preferably satisfies the followingconditional expression (8):

0.05<D34/f<0.2  (8)

When the imaging lens satisfies the conditional expression (8), it ispossible to secure a back focal length while reducing the size of theimaging lens. Moreover, when the imaging lens satisfies the conditionalexpression (8), it is also possible to satisfactorily correctastigmatism and a field curvature. When the value exceeds the upperlimit of “0.2”, although it is advantageous for downsizing of theimaging lens, in the astigmatism, a tangential image surface curves tothe image plane side and an astigmatic difference increases, and theimage-forming surface curves to a plus direction (to the image planeside), so that it is difficult to obtain satisfactory image-formingperformance. In addition, the back focal length is short, so that it isdifficult to secure space to dispose an insert such as an infraredcut-off filter.

On the other hand, when the value is below the lower limit of “0.05”,although it is easy to secure the back focal length, in the astigmatism,the tangential image surface curves to the object side and theastigmatic difference increases, and the image-forming surface alsocurves in a minus direction (to the object side). In addition, thechromatic aberration of magnification for an off-axis light beam isinsufficiently corrected at image periphery (an image-forming point at ashort wavelength moves in a direction to be close to the optical axisrelative to an image-forming point at a reference wavelength), so thatit is difficult to obtain satisfactory image-forming performance.

According to a fifth aspect of the invention, when the whole lens systemhas a focal length f and the first lens has a focal length f1, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (9):

0.5<f1/f<2.0  (9)

When the imaging lens satisfies the conditional expression (9), it ispossible to restrain a chromatic aberration, a coma aberration, and adistortion within satisfactory ranges in a balanced manner whiledownsizing the imaging lens. When the value exceeds the upper limit of“2.0”, since the first lens has weak refractive power relative to therefractive power of the whole lens system, it is easy to secure the backfocal length, but it is difficult to reduce the size of the imaginglens. In addition, inner coma aberration for off-axis light beamsincreases, and the distortion increases in the plus direction, so thatit is difficult to obtain satisfactory image-forming performance. On theother hand, when the value is below the lower limit of “0.5”, althoughit is advantageous for downsizing of the imaging lens, it is difficultto secure the back focal length. In addition, inner coma aberration isgenerated for off-axis light beams and both axial and off-axis chromaticaberrations are insufficiently corrected, so that it is difficult toobtain satisfactory image-forming performance.

According to a sixth aspect of the invention, when the first lens has afocal length f1 and the second lens has a focal length f2, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expression (10):

−4<f2/f1<−0.5  (10)

When the imaging lens satisfies the conditional expression (10), it ispossible to restrain the astigmatism, the chromatic aberration, and thedistortion within satisfactory ranges, while reducing the size of theimaging lens. When the value exceeds the upper limit of “−0.5”, thesecond lens has strong negative refractive power relative to thepositive refractive power of the first lens. Accordingly, although it iseasy to secure the back focal length, it is difficult to reduce the sizeof the imaging lens. As for correction of aberrations, it isadvantageous to correct both axial and off-axis chromatic aberrations ata short wavelength relative to those at a reference wavelength, but inthe astigmatism, a sagittal image surface curves to the object side andthe astigmatic difference increases. Moreover, the distortion increasesin a plus direction. For this reason, it is difficult to obtainsatisfactory image-forming performance.

On the other hand, when the value is below the lower limit of “−4”,although it is advantageous for downsizing of the imaging lens, theaxial chromatic aberration is insufficiently corrected (a focal point ata short wavelength moves to the object side relative to a focal point ata reference wavelength) and the off-axis chromatic aberration ofmagnification is also insufficiently corrected. In addition, theimage-forming surface curves to the object side and the distortionincreases in the minus direction. Therefore, also in this case, it isdifficult to obtain satisfactory image-forming performance.

According to a seventh aspect of the invention, when the first lens hasa focal length f1 and the third lens has a focal length f3, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expression (11):

0.5<f3/f1<4  (11)

When the imaging lens satisfies the conditional expression (11), it ispossible to satisfactorily correct the field curvature, the chromaticaberration, and the distortion, while reducing the size of the imaginglens. When the value exceeds the upper limit of “4”, the third lens hasrelatively weak refractive power. Therefore, although it is advantageousfor correction of the chromatic aberration at a short wavelengthrelative to that at a reference wavelength, the image-forming surfacecurves to the image plane side and the distortion increases in the plusdirection, so that it is difficult to obtain satisfactory image-formingperformance. In addition, it is also difficult to reduce the size of theimaging lens. On the other hand, when the value is below the lower limitof “0.5”, the third lens has relatively strong refractive power.Therefore, although it is advantageous for correction of the astigmatismand the distortion, the axial chromatic aberration and the off-axischromatic aberration of magnification are insufficiently corrected, sothat it is difficult to obtain satisfactory image-forming performance.Moreover, it is difficult to secure the back focal length.

According to an eighth aspect of the invention, when a composite focallength of the fourth lens and the fifth lens is f45 and a compositefocal length of the sixth lens and the seventh lens is f67, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expression (12):

0.5<f45/f67<5  (12)

When the imaging lens satisfies the conditional expression (12), it ispossible to restrain the field curvature, the distortion, and thechromatic aberration within satisfactory ranges in a balanced manner.When the value exceeds the upper limit of “5”, although it isadvantageous for correction of the axial and the off-axis chromaticaberrations at a short wavelength relative to the reference wavelength,the image-forming surface curves to the object side, and the distortionincreases in the plus direction. For this reason, it is difficult toobtain satisfactory image-forming performance. On the other hand, whenthe value is below the lower limit of “0.5”, although it is advantageousfor correction of the distortion, the image-forming surface curves tothe image plane side, and the astigmatic difference increases. For thisreason, it is difficult to obtain satisfactory image-formingperformance.

According to a ninth aspect of the invention, when the whole lens systemhas a focal length f, the composite focal length of the fourth lens andthe fifth lens is f45, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(13):

−7<f45/f<−1.5  (13)

When the imaging lens satisfies the conditional expression (13), it ispossible to satisfactorily correct the chromatic aberration and theastigmatism, while securing flatness of the image-forming surface. Whenthe value exceeds the upper limit of “−1.5”, although it is advantageousfor correcting the chromatic aberration, it is difficult to secure theflatness of the image-forming surface. On the other hand, when the valueis below the lower limit of “−7”, the astigmatic difference increasesand it is difficult to secure the flatness of the image-forming surface.Moreover, it is difficult to correct the chromatic aberration and it isdifficult to obtain satisfactory image-forming performance.

In order to more satisfactorily correct the chromatic aberration and theastigmatism while securing the flatness of the image-forming surface,according to a tenth aspect of the invention, the imaging lens havingthe above-described configuration preferably satisfies the followingconditional expression (13A):

−5<f45/f<−1.5  (13A)

According to an eleventh aspect of the invention, when the fourth lenshas a focal length f4 and the fifth lens has a focal length f5, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (14):

−8<f4/f5<−1.5  (14)

When the imaging lens satisfies the conditional expression (14), it ispossible to restrain the field curvature, the astigmatism, the chromaticaberration, and the distortion within preferred ranges in a balancedmanner. When the value exceeds the upper limit of “−1.5”, the axialchromatic aberration and the off-axis chromatic aberration ofmagnification increase and the astigmatic difference increases, so thatit is difficult to obtain satisfactory image-forming performance. On theother hand, when the value is below the lower limit of “−8”, the fourthlens has weak positive refractive power relative to the negativerefractive power of the fifth lens. Therefore, although it isadvantageous for correcting the axial and the off-axis chromaticaberrations, the astigmatic difference for the off-axis light beamsincreases and the distortion increases in the plus direction, so that itis difficult to obtain satisfactory image-forming performance.

According to a twelfth aspect of the invention, when the whole lenssystem has a focal length f and the fourth lens has a focal length f4,the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (15):

2<f4/f<15  (15)

When the imaging lens satisfies the conditional expression (15), it ispossible to satisfactorily correct the chromatic aberration and thefield curvature. When the value exceeds the upper limit of “15”, thefourth lens has weak refractive power relative to the refractive powerof the whole lens system. Therefore, although it is advantageous forcorrection of the chromatic aberration of magnification for off-axislight beams, the image-forming surface curves to the object side, sothat it is difficult to obtain satisfactory image-forming performance.On the other hand, when the value is below the lower limit of “2”, theaxial chromatic aberration and the chromatic aberration of magnificationare both insufficiently corrected, and the image-forming surface curvesto the image plane side, so that, also in this case, it is difficult toobtain satisfactory image-forming performance.

According to a thirteenth aspect of the invention, the imaging lenshaving the above-described configuration has the fifth lens, which hasan object-side surface having negative curvature radius and an imageplane-side surface having positive curvature radius. When the curvatureradius of the object-side surface of the fifth lens is R5 f and thecurvature radius of the image plane-side surface of the fifth lens is R5r, the imaging lens preferably satisfies the following conditionalexpression (16):

−15<R5f/R5r<−3  (16)

When the imaging lens satisfies the conditional expression (16), it ispossible to satisfactorily correct the chromatic aberration ofmagnification and the astigmatism, while securing the flatness of theimage-forming surface. When the value exceeds the upper limit of “−3”,the sagittal image surface in the astigmatism curves to the object sideat the periphery of the image, so that it is difficult to secure theflatness of the image-forming surface. In addition, the chromaticaberration of magnification is insufficiently corrected, so that it isdifficult to obtain satisfactory image-forming performance. On the otherhand, when the value is below the lower limit of “−15”, although it isadvantageous for correction of the chromatic aberration ofmagnification, the tangential image surface in the astigmatism curves tothe image plane side, so that the astigmatic difference increases and itis difficult to obtain satisfactory image-forming performance.

According to a fourteenth aspect of the invention, when the whole lenssystem has a focal length f and the seventh lens has a focal length f7,the imaging lens preferably satisfies the following conditionalexpression (17):

−8<f7/f<−1  (17)

When the imaging lens satisfies the conditional expression (17), it ispossible to restrain the coma aberration, the chromatic aberration, andthe distortion within preferred ranges in a balanced manner. When thevalue exceeds the upper limit of “−1”, although it is advantageous forcorrection of the axial chromatic aberration, the inner coma aberrationincreases for the off-axis light beams and the chromatic aberration ofmagnification increases, so that it is difficult to obtain satisfactoryimage-forming performance. On the other hand, when the value is belowthe lower limit of “−8”, although it is advantageous for correction ofthe chromatic aberration of magnification, outer coma aberrationincreases for the tangential image surface of off-axis light beams, andthe distortion increases in the plus direction. For this reason, it isdifficult to obtain satisfactory image-forming performance.

According to a fifteenth aspect of the invention, in order to morepreferably correct the coma aberration, the chromatic aberration, andthe distortion, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(17A):

−6<f7/f<−1  (17A)

According to the imaging lens of the invention, it is possible toprovide a small imaging lens suitable for mounting in a small-sizedcamera, while having high resolution with satisfactorily correctedaberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 1 according to an embodiment of theinvention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 2 according to the embodiment of theinvention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 3 according to the embodiment of theinvention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 4 according to the embodiment ofthe invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 5 according to the embodiment ofthe invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13;

FIG. 15 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 13 FIG. 16shows a sectional view of a schematic configuration of an imaging lensin Numerical Data Example 6 according to the embodiment of theinvention;

FIG. 17 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 16; and

FIG. 18 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, an embodiment of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, 13 and 16 are schematic sectional views of imaginglenses in Numerical Data Examples 1 to 6 according to the embodiment,respectively. Since a basic lens configuration is the same among thoseNumerical Data Examples, the lens configuration of the embodiment willbe described with reference to the illustrative sectional view ofNumerical Data Example 1.

As shown in FIG. 1, the imaging lens of the embodiment includes a firstlens group G1 having positive refractive power, a second lens group G2having negative refractive power, and a third lens group G3 havingnegative refractive power, arranged in the order from an object side toan image plane side. Between the third lens group G3 and an image planeIM of an imaging element, there may be provided a filter 10. The filter10 may be optionally omitted.

The first lens group G1 includes a first lens L1 having positiverefractive power, an aperture stop ST, a second lens L2 having negativerefractive power, and a third lens L3 having positive refractive power,arranged in the order from the object side. The first lens L1 is formedin a shape such that a curvature radius r1 of an object-side surfacethereof is positive and a curvature radius r2 of an image plane-sidesurface thereof is negative, and has a shape of a biconvex lens near anoptical axis X. Here, the shape of the first lens L1 is not limited tothe one in Numerical Data Example 1. The shape of the first lens L1 canbe any as long as the curvature radius r1 of the object-side surfacethereof is positive, and can be a shape such that the curvature radiusr2 of the image plane-side surface thereof is positive, i.e., a shape ofa meniscus lens directing a convex surface thereof to the object sidenear the optical axis X.

The second lens L2 is formed in a shape such that a curvature radius r4of an object-side surface thereof and a curvature radius r5 of an imageplane-side surface thereof are both positive, and has a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. The shape of the second lens L2 is not limited tothe one in Numerical Data Example 1. The shape of the second lens L2 canbe any as long as the curvature radius r5 of the image plane-sidesurface thereof is positive, and can be a shape such that the curvatureradius r4 of the object-side surface thereof is negative, i.e., a shapeof a biconcave lens near the optical axis X.

The third lens L3 is formed in a shape such that a curvature radius r6of an object-side surface thereof is positive and a curvature radius r7of an image plane-side surface thereof is negative, and has a shape of abiconvex lens near the optical axis X.

The second lens group G2 includes a fourth lens L4 having positiverefractive power, and a fifth lens L5 having negative refractive power,arranged in the order from the object side. Among them, the fourth lensL4 is formed in a shape such that a curvature radius r8 of anobject-side surface thereof and a curvature radius r9 of an imageplane-side surface thereof are both negative, and has a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X.

The fifth lens L5 is formed in a shape such that a curvature radius r10of an object-side surface thereof is negative and a curvature radius r11of an image plane-side surface thereof is positive, and has a shape of abiconcave lens near the optical axis X. Here, the shape of the fifthlens L5 is not limited to the one in Numerical Data Example 1. The shapeof the fifth lens L5 can be any as long as the curvature radius r11 ofthe image plane-side surface thereof is positive. The shape of the fifthlens L5 can be formed in a shape such that the curvature radius r10 ofthe object-side surface thereof is positive, i.e., a shape of a meniscuslens directing a convex surface thereof to the object side near theoptical axis X.

The third lens group G3 includes a sixth lens L6 having negativerefractive power and a seventh lens L7 having negative refractive power,arranged in the order from the object side. The sixth lens L6 is formedin a shape such that a curvature radius r12 of an object-side surfacethereof and a curvature radius r13 of an image plane-side surfacethereof are both positive, and has a shape of a meniscus lens directinga convex surface thereof to the object side near the optical axis X. Theseventh lens L7 is formed in a shape such that a curvature radius r14 ofan object-side surface thereof and a curvature radius r15 of an imageplane-side surface thereof are both positive, and has a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X.

Furthermore, in each of the sixth lens L6 and the seventh lens L7, theobject-side surface thereof and the image plane-side surface thereof areformed as aspheric shapes having inflexion points. More specifically,each of the sixth lens L6 and the seventh lens L7 is formed in a shapeso as to have negative refractive power near the optical axis X and havestronger positive refractive power as it goes to the lens periphery.With those shapes of the sixth lens L6 and the seventh lens L7, it ispossible to satisfactorily correct axial chromatic aberration as well asoff-axis chromatic aberration of magnification. In addition, it is alsopossible to suitably restrain incident angles of light beams emittedfrom the imaging lens to the image plane IM within the range of chiefray angle (CRA).

Here, according to the embodiment, the sixth lens L6 and the seventhlens L7 have their both object-side surfaces and image plane-sidesurfaces formed as aspheric shapes having inflexion points. However, itis not necessary to form both of those surfaces as aspheric shapeshaving inflexion points. Even when each of those lenses has an asphericsurface having an inflexion point only on one side surface, it is stillpossible to form both or one of those lenses in shapes so as to havenegative refractive power near the optical axis X and have strongpositive refractive power as it goes to the lens peripheries thereof. Inaddition, depending on required optical performances and degree ofdownsizing of the imaging lens, it is not always necessary to provide aninflexion point in the sixth lens L6 and the seventh lens L7.

The imaging lens of the embodiment satisfies the following conditionalexpressions (1) to (17):

40<νd1<75  (1)

20<νd2<35  (2)

40<νd3<75  (3)

20<νd4<35  (4)

20<νd5<35  (5)

40<νd6<75  (6)

40<νd7<75  (7)

0.05<D34/f<0.2  (8)

0.5<f1/f<2.0  (9)

−4<f2/f1<−0.5  (10)

0.5<f3/f1<4  (11)

0.5<f45/f67<5  (12)

−7<f45/f<−1.5  (13)

−8<f4/f5<−1.5  (14)

2<f4/f<15  (15)

−15<R5f/R5r<−3  (16)

−8<f7/f<−1  (17)

In the above conditional expressions:

νd1: Abbe's number of a first lens L1νd2: Abbe's number of a second lens L2νd3: Abbe's number of a third lens L3νd4: Abbe's number of a fourth lens L4νd5: Abbe's number of a fifth lens L5νd6: Abbe's number of a sixth lens L6νd7: Abbe's number of a seventh lens L7f: Focal length of the whole lens systemf1: Focal length of the first lens L1f2: Focal length of the second lens L2f3: Focal length of the third lens L3f4: Focal length of the fourth lens L4f5: Focal length of the fifth lens L5f7: Focal length of the seventh lens L7f45: Composite focal length of the fourth lens L4 and the fifth lens L5f67: Composite focal length of the sixth lens L6 and the seventh lens L7D34: Distance on an optical axis X between the third lens L3 and thefourth lens L4R5 f: Curvature radius of an object-side surface of the fifth lens L5R5 r: Curvature radius of an image plane-side surface of the fifth lensL5

The imaging lens of the embodiment satisfies the following conditionalexpressions (13A) and (17A) to further satisfactorily correct theaberrations:

−5<f45/f<−1.5  (13A)

−6<f7/f<−1  (17A)

Here, it is not necessary to satisfy all of the conditional expressions,and it is achievable to obtain an effect corresponding to the respectiveconditional expressions when any single one of the conditionalexpressions is individually satisfied.

In the embodiment, all lens surfaces of the respective lenses are formedas aspheric surfaces. When the aspheric surfaces applied to the lenssurfaces have an axis Z in a direction of the optical axis X, a height Hin a direction perpendicular to the optical axis X, a conicalcoefficient k, and aspheric coefficients A₄, A₆, A₈, A₁₀, A₁₂, A₁₄, andA₁₆, a shape of the aspheric surfaces of the lens surfaces is expressedas follows:

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\mspace{14mu} \frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F number, and ωrepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, r represents a curvatureradius, d represents a distance on the optical axis between lenssurfaces (surface spacing), nd represents a refractive index for a dline (a reference wavelength), and νd represents an Abbe's number forthe d line, respectively. Here, aspheric surfaces are indicated withsurface numbers i affixed with * (asterisk).

Numerical Data Example 1

Basic data are shown below.

f=9.57 mm, Fno=2.4, ω=32.1°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 3.3181.213 1.5346 56.1 (=νd1)  2* −39.261 −0.025  3 (Stop) ∞ 0.116  4* 33.9840.298 1.6355 24.0 (=νd2)  5* 6.127 0.059  6* 10.639 0.655 1.5346 56.1(=νd3)  7* −62.349 0.949 (=D34)  8* −3.442 0.562 1.6355 24.0 (=νd4)  9*−3.467 0.098 10* −42.006 (=R5f) 0.647 1.6355 24.0 (=νd5) 11*   13.772(=R5r) 0.571 12* 9.539 1.099 1.5346 56.1 (=νd6) 13* 6.640 0.526 14*12.045 1.544 1.5346 56.1 (=νd7) 15* 4.642 0.440 16 ∞ 0.300 1.5168 64.217 ∞ 1.063 (Image ∞ plane) Aspheric Surface Data First Surface k =0.000, A₄ = −2.995E−03, A₆ = −1.855E−04, A₈ = −2.472E−04, A₁₀ =−3.907E−06, A₁₂ = −5.270E−07, A₁₄ = 2.761E−07, A₁₆ = −1.217E−09 SecondSurface k = 0.000, A₄ = 1.174E−02, A₆ = −1.391E−02, A₈ = 5.212E−03, A₁₀= −9.563E−04, A₁₂ = 7.839E−05, A₁₄ = −2.213E−06, A₁₆ = 5.641E−08 FourthSurface k = 0.000, A₄ = 1.333E−02, A₆ = −2.008E−02, A₈ = 7.838E−03, A₁₀= −1.302E−03, A₁₂ = 7.691E−05, A₁₄ = 5.904E−07, A₁₆ = −5.003E−07 FifthSurface k = 0.000, A₄ = 6.851E−03, A₆ = −1.313E−02, A₈ = 3.616E−03, A₁₀= −2.531E−04, A₁₂ = −2.370E−05, A₁₄ = −1.000E−05, A₁₆ = 1.564E−06 SixthSurface k = 0.000, A₄ = 1.103E−02, A₆ = −2.591E−03, A₈ = 1.170E−03, A₁₀= −4.329E−05, A₁₂ = −5.911E−06, A₁₄ = 2.463E−06, A₁₆ = −1.368E−06Seventh Surface k = 0.000, A₄ = −1.065E−03, A₆ = 2.211E−03, A₈ =8.593E−04, A₁₀ = −4.613E−04, A₁₂ = 7.895E−05, A₁₄ = 7.220E−06, A₁₆ =−5.043E−06 Eighth Surface k = 0.000, A₄ = −1.547E−02, A₆ = 2.513E−03, A₈= −2.149E−05, A₁₀ = −2.485E−04, A₁₂ = −1.856E−05, A₁₄ = 1.073E−07, A₁₆ =1.527E−06 Ninth Surface k = 0.000, A₄ = −6.920E−03, A₆ = 1.871E−03, A₈ =8.894E−05, A₁₀ = 1.388E−06, A₁₂ = −2.970E−05, A₁₄ = −1.020E−06, A₁₆ =2.309E−06 Tenth Surface k = 0.000, A₄ = −8.230E−03, A₆ = −9.253E−04, A₈= −7.779E−06, A₁₀ = 6.194E−06, A₁₂ = −1.505E−06, A₁₄ = 5.207E−07, A₁₆ =−3.481E−08 Eleventh Surface k = 0.000, A₄ = −1.020E−02, A₆ = −6.061E−04,A₈ = 1.202E−04, A₁₀ = 1.683E−06, A₁₂ = 1.154E−07, A₁₄ = −4.525E−08, A₁₆= 7.646E−11 Twelfth Surface k = 0.000, A₄ = −1.374E−02, A₆ = −3.962E−04,A₈ = −3.784E−05, A₁₀ = −2.372E−06, A₁₂ = 1.515E−07, A₁₄ = 2.223E−08, A₁₆= −2.404E−09 Thirteenth Surface k = 0.000, A₄ = −1.172E−02, A₆ =2.665E−05, A₈ = 2.272E−05, A₁₀ = −1.026E−06, A₁₂ = −5.260E−09, A₁₄ =1.463E−09, A₁₆ = −2.585E−11 Fourteenth Surface k = 0.000, A₄ =−2.216E−02, A₆ = 1.317E−03, A₈ = −2.194E−05, A₁₀ = −2.470E−07, A₁₂ =6.753E−10, A₁₄ = 1.105E−10, A₁₆ = 1.524E−11 Fifteenth Surface k =−1.551E+01, A₄ = −9.918E−03, A₆ = 3.875E−04, A₈ = −1.268E−05, A₁₀ =1.234E−07, A₁₂ = 9.762E−09, A₁₄ = −5.202E−10, A₁₆ = 6.871E−12 f1 = 5.78mm f2 = −11.81 mm f3 = 17.05 mm f4 = 97.25 mm f5 = −16.25 mm f6 = −47.08mm f7 = −15.23 mm f45 = −18.21 mm f67 = −11.44 mm

The values of the respective conditional expressions are as follows:

D34/f=0.10

f1/f=0.60f2/f1=−2.04f3/f1=2.95f4/f=10.16f7/f=−1.59f45/f=−1.90f45/f67=1.59f4/f5=−5.99

R5 f/R5 r=−3.05

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length in air for the filter 10) is 10.01 mm, and downsizingof the imaging lens is attained.

FIG. 2 shows a lateral aberration that corresponds to a ratio H of eachimage height to the maximum image height (hereinafter referred to as“image height ratio H”), which is divided into a tangential directionand a sagittal direction (which is the same in FIGS. 5, 8, 11, 14, and17). Furthermore, FIG. 3 shows a spherical aberration (mm), astigmatism(mm), and a distortion (%), respectively in the imaging lens ofNumerical Data Example 1. In the aberration diagrams, for the lateralaberration diagrams and spherical aberration diagrams, aberrations ateach wavelength, i.e. a g line (436 nm), an e line (546 nm), and a Cline (656 nm) are indicated. In the astigmatism diagrams, an aberrationon a sagittal image surface S and an aberration on a tangential imagesurface T are respectively indicated (which are the same in FIGS. 6, 9,12, 15, and 18). As shown in FIGS. 2 and 3, according to the imaginglens of Numerical Data Example 1, the aberrations are satisfactorilycorrected.

Numerical Data Example 2

Basic data are shown below.

f=7.06 mm, Fno=2.1, ω=40.4°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 3.3761.222 1.5346 56.1 (=νd1)  2* −42.517 −0.050  3 (Stop) ∞ 0.113  4* 22.6000.300 1.6355 24.0 (=νd2)  5* 5.867 0.030  6* 9.704 0.550 1.5346 56.1(=νd3)  7* −49.191 0.902 (=D34)  8* −3.593 0.513 1.6355 24.0 (=νd4)  9*−3.349 0.009 10* −140.096 (=R5f) 0.797 1.6355 24.0 (=νd5) 11*    12.288(=R5r) 0.370 12* 6.574 1.204 1.5346 56.1 (=νd6) 13* 5.977 0.384 14*9.315 1.525 1.5346 56.1 (=νd7) 15* 4.593 0.440 16 ∞ 0.300 1.5168 64.2 17∞ 0.345 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000,A₄ = −3.965E−03, A₆ = −3.163E−04, A₈ = −2.704E−04, A₁₀ = −8.336E−06, A₁₂= −1.271E−06, A₁₄ = 1.969E−07, A₁₆ = 5.583E−08 Second Surface k = 0.000,A₄ = 1.203E−02, A₆ = −1.415E−02, A₈ = 5.161E−03, A₁₀ = −9.595E−04, A₁₂ =8.081E−05, A₁₄ = −1.836E−06, A₁₆ = −4.840E−07 Fourth Surface k = 0.000,A₄ = 1.365E−02, A₆ = −1.977E−02, A₈ = 7.890E−03, A₁₀ = −1.308E−03, A₁₂ =6.801E−05, A₁₄ = −2.846E−06, A₁₆ = −1.083E−07 Fifth Surface k = 0.000,A₄ = 7.248E−03, A₆ = −1.265E−02, A₈ = 3.664E−03, A₁₀ = −2.756E−04, A₁₂ =−3.387E−05, A₁₄ = −1.169E−05, A₁₆ = 9.552E−07 Sixth Surface k = 0.000,A₄ = 1.236E−02, A₆ = −2.626E−03, A₈ = 1.167E−03, A₁₀ = −4.452E−05, A₁₂ =−1.290E−05, A₁₄ = −1.228E−06, A₁₆ = −1.707E−06 Seventh Surface k =0.000, A₄ = −1.956E−03, A₆ = 2.108E−03, A₈ = 7.792E−04, A₁₀ =−5.058E−04, A₁₂ = 6.916E−05, A₁₄ = 7.074E−06, A₁₆ = −4.781E−06 EighthSurface k = 0.000, A₄ = −1.579E−02, A₆ = 1.663E−03, A₈ = 7.286E−05, A₁₀= −1.883E−04, A₁₂ = −1.452E−06, A₁₄ = 2.090E−06, A₁₆ = 5.824E−07 NinthSurface k = 0.000, A₄ = −7.842E−03, A₆ = 1.896E−03, A₈ = 1.180E−04, A₁₀= 1.366E−05, A₁₂ = −2.640E−05, A₁₄ = 2.516E−07, A₁₆ = 2.843E−06 TenthSurface k = 0.000, A₄ = −6.684E−03, A₆ = −1.414E−03, A₈ = −7.300E−05,A₁₀ = −1.783E−06, A₁₂ = −1.157E−06, A₁₄ = 4.678E−07, A₁₆ = −3.611E−07Eleventh Surface k = 0.000, A₄ = −9.334E−03, A₆ = −7.328E−04, A₈ =1.127E−04, A₁₀ = 1.688E−06, A₁₂ = 1.388E−07, A₁₄ = −4.840E−08, A₁₆ =−1.301E−09 Twelfth Surface k = 0.000, A₄ = −1.284E−02, A₆ = −3.041E−04,A₈ = −3.322E−06, A₁₀ = 1.745E−06, A₁₂ = 4.153E−07, A₁₄ = 2.627E−08, A₁₆= −4.103E−09 Thirteenth Surface k = 0.000, A₄ = −1.036E−02, A₆ =−4.358E−05, A₈ = 2.821E−07, A₁₀ = −4.786E−07, A₁₂ = 3.614E−08, A₁₄ =1.008E−09, A₁₆ = −1.640E−10 Fourteenth Surface k = 0.000, A₄ =−1.983E−02, A₆ = 1.289E−03, A₈ = −2.257E−05, A₁₀ = −2.681E−07, A₁₂ =−5.283E−10, A₁₄ = 3.760E−11, A₁₆ = 1.055E−11 Fifteenth Surface k =−4.229, A₄ = −8.594E−03, A₆ = 4.390E−04, A₈ = −1.275E−05, A₁₀ =1.463E−07, A₁₂ = 1.051E−08, A₁₄ = −5.125E−10, A₁₆ = 6.372E−12 f1 = 5.91mm f2 = −12.56 mm f3 = 15.21 mm f4 = 42.80 mm f5 = −17.74 mm f6 =−415.47 mm f7 = −19.10 mm f45 = −28.14 mm f67 = −19.32 mm

The values of the respective conditional expressions are as follows:

D34/f=0.13

f1/f=0.84f2/f1=−2.13f3/f1=2.58f4/f=6.07f7/f=−2.71f45/f=−3.99f45/f67=1.46f4/f5=−2.41

R5 f/R5 r=−11.40

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length in air for the filter 10) is 8.85 mm, and downsizing ofthe imaging lens is attained.

FIG. 5 shows the lateral aberration that corresponds to the image heightratio H, and FIG. 6 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively, of the imaging lens in NumericalData Example 2. As shown in FIGS. 5 and 6, also according to the imaginglens of Numerical Data Example 2, the aberrations are satisfactorilycorrected.

Numerical Data Example 3

Basic data are shown below.

f=6.53 mm, Fno=2.3, ω=42.6°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 3.7471.096 1.5346 56.1 (=νd1)  2* −48.045 −0.033  3 (Stop) ∞ 0.103  4* 12.7360.319 1.6355 24.0 (=νd2)  5* 5.015 0.064  6* 7.630 0.448 1.5346 56.1(=νd3)  7* −38.331 0.913 (=D34)  8* −3.541 0.410 1.6355 24.0 (=νd4)  9*−3.373 0.048 10* −174.656 (=R5f) 0.853 1.6355 24.0 (=νd5) 11*    11.683(=R5r) 0.192 12* 5.520 1.236 1.5346 56.1 (=νd6) 13* 5.007 0.379 14*5.697 1.681 1.5346 56.1 (=νd7) 15* 3.800 0.500 16 ∞ 0.300 1.5168 64.2 17∞ 0.199 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000,A₄ = −4.897E−03, A₆ = −6.882E−04, A₈ = −2.528E−04, A₁₀ = 1.272E−05, A₁₂= 7.916E−07, A₁₄ = −7.723E−07, A₁₆ = −1.108E−07 Second Surface k =0.000, A₄ = 1.231E−02, A₆ = −1.421E−02, A₈ = 5.376E−03, A₁₀ =−1.049E−03, A₁₂ = 9.008E−05, A₁₄ = −2.426E−05, A₁₆ = −3.424E−07 FourthSurface k = 0.000, A₄ = 1.223E−02, A₆ = −1.934E−02, A₈ = 8.101E−03, A₁₀= −1.519E−03, A₁₂ = 2.061E−05, A₁₄ = −2.114E−05, A₁₆ = 3.333E−06 FifthSurface k = 0.000, A₄ = 6.110E−03, A₆ = −1.198E−02, A₈ = 3.663E−03, A₁₀= −4.140E−04, A₁₂ = −1.961E−04, A₁₄ = 1.129E−05, A₁₆ = 2.827E−06 SixthSurface k = 0.000, A₄ = 1.789E−02, A₆ = −2.105E−03, A₈ = 1.206E−03, A₁₀= −8.461E−05, A₁₂ = 8.494E−06, A₁₄ = −5.253E−08, A₁₆ = −2.102E−06Seventh Surface k = 0.000, A₄ = 9.372E−04, A₆ = 1.895E−03, A₈ =8.351E−04, A₁₀ = −4.931E−04, A₁₂ = 1.468E−04, A₁₄ = 4.910E−05, A₁₆ =−2.035E−05 Eighth Surface k = 0.000, A₄ = −1.456E−02, A₆ = 1.261E−03, A₈= 8.563E−05, A₁₀ = −1.452E−04, A₁₂ = 5.646E−06, A₁₄ = 6.631E−06, A₁₆ =5.902E−07 Ninth Surface k = 0.000, A₄ = −1.100E−02, A₆ = 1.780E−03, A₈ =2.576E−04, A₁₀ = 3.745E−05, A₁₂ = −2.163E−05, A₁₄ = 3.806E−06, A₁₆ =3.019E−06 Tenth Surface k = 0.000, A₄ = −7.203E−03, A₆ = −9.866E−04, A₈= −2.549E−04, A₁₀ = 1.481E−05, A₁₂ = 2.102E−06, A₁₄ = 1.421E−06, A₁₆ =−7.331E−07 Eleventh Surface k = 0.000, A₄ = −5.885E−03, A₆ = −1.203E−03,A₈ = 1.088E−04, A₁₀ = 3.387E−06, A₁₂ = 3.204E−07, A₁₄ = −4.440E−08, A₁₆= −3.595E−09 Twelfth Surface k = 0.000, A₄ = −1.182E−02, A₆ =−2.329E−04, A₈ = −1.016E−05, A₁₀ = 1.296E−06, A₁₂ = 4.016E−07, A₁₄ =2.805E−08, A₁₆ = −4.028E−09 Thirteenth Surface k = 0.000, A₄ =−1.028E−02, A₆ = 2.672E−05, A₈ = 2.750E−07, A₁₀ = 1.701E−07, A₁₂ =−4.949E−08, A₁₄ = 2.449E−09, A₁₆ = −1.387E−11 Fourteenth Surface k =0.000, A₄ = −2.193E−02, A₆ = 1.281E−03, A₈ = −2.166E−05, A₁₀ =−2.434E−07, A₁₂ = −3.365E−10, A₁₄ = 1.103E−11, A₁₆ = 7.932E−12 FifteenthSurface k = −4.029, A₄ = −6.845E−03, A₆ = 2.887E−04, A₈ = −1.088E−05,A₁₀ = 2.093E−07, A₁₂ = 1.102E−08, A₁₄ = −5.572E−10, A₁₆ = 6.186E−12 f1 =6.55 mm f2 = −13.23 mm f3 = 11.94 mm f4 = 57.35 mm f5 = −17.20 mm f6 =−625.60 mm f7 = −30.89 mm f45 = −23.38 mm f67 = −31.53 mmThe values of the respective conditional expressions are as follows:

D34/f=0.14

f1/f=1.00f2/f1=−2.02f3/f1=1.82f4/f=8.78f7/f=−4.73f45/f=−3.58f45/f67=0.74f4/f5=−3.33

R5 f/R5 r=−14.95

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length in air for the filter 10) is 8.61 mm, and downsizing ofthe imaging lens is attained.

FIG. 8 shows the lateral aberration that corresponds to the image heightratio H, and FIG. 9 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively, of the imaging lens in NumericalData Example 3. As shown in FIGS. 8 and 9, according to the imaging lensof Numerical Data Example 3, the aberrations are satisfactorilycorrected.

Numerical Data Example 4

Basic data are shown below.

f=7.35 mm, Fno=2.3, ω=39.2°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 3.2841.097 1.5346 56.1 (=νd1)  2* −41.278 −0.061  3 (Stop) ∞ 0.104  4* 16.3390.299 1.6355 24.0 (=νd2)  5* 6.448 0.078  6* 15.586 0.602 1.5346 56.1(=νd3)  7* −30.644 0.812 (=D34)  8* −3.447 0.534 1.6355 24.0 (=νd4)  9*−3.472 0.034 10* −44.466 (=R5f) 0.887 1.6355 24.0 (=νd5) 11*   14.579(=R5r) 0.392 12* 7.094 1.189 1.5346 56.1 (=νd6) 13* 5.783 0.373 14*9.726 1.627 1.5346 56.1 (=νd7) 15* 4.323 0.440 16 ∞ 0.300 1.5168 64.2 17∞ 0.328 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000,A₄ = −4.169E−03, A₆ = −4.078E−04, A₈ = −3.491E−04, A₁₀ = −2.123E−05, A₁₂= 2.610E−07, A₁₄ = 6.742E−07, A₁₆ = 1.211E−07 Second Surface k = 0.000,A₄ = 1.162E−02, A₆ = −1.409E−02, A₈ = 5.302E−03, A₁₀ = −9.313E−04, A₁₂ =7.885E−05, A₁₄ = −7.132E−06, A₁₆ = 2.874E−07 Fourth Surface k = 0.000,A₄ = 1.251E−02, A₆ = −1.964E−02, A₈ = 7.896E−03, A₁₀ = −1.291E−03, A₁₂ =8.829E−05, A₁₄ = −2.178E−06, A₁₆ = −3.084E−06 Fifth Surface k = 0.000,A₄ = 7.229E−03, A₆ = −1.230E−02, A₈ = 3.715E−03, A₁₀ = −2.866E−04, A₁₂ =−3.531E−05, A₁₄ = −1.328E−05, A₁₆ = −6.873E−07 Sixth Surface k = 0.000,A₄ = 1.555E−02, A₆ = −2.281E−03, A₈ = 1.218E−03, A₁₀ = −3.654E−05, A₁₂ =−1.982E−05, A₁₄ = −2.664E−06, A₁₆ = −1.933E−06 Seventh Surface k =0.000, A₄ = −1.141E−03, A₆ = 1.452E−03, A₈ = 7.450E−04, A₁₀ =−5.151E−04, A₁₂ = 7.445E−05, A₁₄ = 9.947E−06, A₁₆ = −5.225E−06 EighthSurface k = 0.000, A₄ = −1.467E−02, A₆ = 1.999E−03, A₈ = 4.477E−05, A₁₀= −2.515E−04, A₁₂ = 5.378E−06, A₁₄ = 3.933E−06, A₁₆ = 8.021E−07 NinthSurface k = 0.000, A₄ = −7.606E−03, A₆ = 2.109E−03, A₈ = 2.004E−04, A₁₀= 2.437E−05, A₁₂ = −2.679E−05, A₁₄ = 3.037E−07, A₁₆ = 3.357E−06 TenthSurface k = 0.000, A₄ = −9.676E−03, A₆ = −1.147E−03, A₈ = −9.354E−05,A₁₀ = −6.363E−06, A₁₂ = −1.932E−06, A₁₄ = 5.625E−07, A₁₆ = −3.675E−07Eleventh Surface k = 0.000, A₄ = −9.125E−03, A₆ = −7.163E−04, A₈ =1.216E−04, A₁₀ = 2.175E−06, A₁₂ = 1.429E−07, A₁₄ = −5.588E−08, A₁₆ =−2.586E−09 Twelfth Surface k = 0.000, A₄ = −1.277E−02, A₆ = −2.629E−04,A₈ = −4.583E−07, A₁₀ = 2.110E−06, A₁₂ = 4.167E−07, A₁₄ = 2.440E−08, A₁₆= −4.222E−09 Thirteenth Surface k = 0.000, A₄ = −1.036E−02, A₆ =−1.347E−04, A₈ = 2.262E−05, A₁₀ = −7.439E−07, A₁₂ = −2.085E−08, A₁₄ =7.659E−10, A₁₆ = 6.534E−11 Fourteenth Surface k = 0.000, A₄ =−1.971E−02, A₆ = 1.286E−03, A₈ = −2.255E−05, A₁₀ = −2.662E−07, A₁₂ =−1.014E−10, A₁₄ = 4.672E−11, A₁₆ = 1.067E−11 Fifteenth Surface k =−5.530, A₄ = −8.680E−03, A₆ = 4.453E−04, A₈ = −1.374E−05, A₁₀ =1.561E−07, A₁₂ = 1.084E−08, A₁₄ = −5.127E−10, A₁₆ = 6.326E−12 f1 = 5.74mm f2 = −16.96 mm f3 = 19.41 mm f4 = 102.88 mm f5 = −17.18 mm f6 =−85.58 mm f7 = −16.26 mm f45 = −19.32 mm f67 = −14.01 mmThe values of the respective conditional expressions are as follows:

D34/f=0.11

f1/f=0.78f2/f1=−2.95f3/f1=3.38f4/f=13.99f7/f=−2.21f45/f=−2.63f45/f67=1.38f4/f5=−5.99

R5 f/R5 r=−3.05

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length in air for the filter 10) is 8.93 mm, and downsizing ofthe imaging lens is attained.

FIG. 11 shows the lateral aberration that corresponds to the imageheight ratio H, and FIG. 12 shows a spherical aberration (mm),astigmatism (mm), and a distortion (%), respectively, of the imaginglens in Numerical Data Example 4. As shown in FIGS. 11 and 12, accordingto the imaging lens of Numerical Data Example 4, the aberrations arealso satisfactorily corrected.

Numerical Data Example 5

Basic data are shown below.

f=8.06 mm, Fno=2.4, ω=36.7°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 3.5191.230 1.5346 56.1 (=νd1)  2* −43.736 −0.036  3 (Stop) ∞ 0.125  4* 47.6760.299 1.6355 24.0 (=νd2)  5* 5.327 0.019  6* 7.830 0.527 1.5346 56.1(=νd3)  7* −42.991 0.915 (=D34)  8* −3.638 0.513 1.6355 24.0 (=νd4)  9*−3.324 0.045 10* −181.880 (=R5f) 0.746 1.6355 24.0 (=νd5) 11*    12.169(=R5r) 0.424 12* 6.735 1.213 1.5346 56.1 (=νd6) 13* 5.708 0.417 14*7.712 1.582 1.5346 56.1 (=νd7) 15* 4.566 0.440 16 ∞ 0.300 1.5168 64.2 17∞ 0.927 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000,A₄ = −3.738E−03, A₆ = −3.235E−04, A₈ = −2.525E−04, A₁₀ = −4.247E−06, A₁₂= 1.297E−07, A₁₄ = 3.837E−07, A₁₆ = 1.477E−09 Second Surface k = 0.000,A₄ = 1.218E−02, A₆ = −1.414E−02, A₈ = 5.175E−03, A₁₀ = −9.562E−04, A₁₂ =8.101E−05, A₁₄ = −1.787E−06, A₁₆ = −2.744E−07 Fourth Surface k = 0.000,A₄ = 1.407E−02, A₆ = −1.966E−02, A₈ = 7.903E−03, A₁₀ = −1.300E−03, A₁₂ =6.905E−05, A₁₄ = −2.305E−06, A₁₆ = −5.934E−07 Fifth Surface k = 0.000,A₄ = 6.942E−03, A₆ = −1.262E−02, A₈ = 3.669E−03, A₁₀ = −2.792E−04, A₁₂ =−3.558E−05, A₁₄ = −1.217E−05, A₁₆ = 1.452E−06 Sixth Surface k = 0.000,A₄ = 1.235E−02, A₆ = −2.659E−03, A₈ = 1.161E−03, A₁₀ = −4.378E−05, A₁₂ =−1.366E−05, A₁₄ = −1.731E−06, A₁₆ = −1.449E−06 Seventh Surface k =0.000, A₄ = −1.528E−03, A₆ = 2.305E−03, A₈ = 8.006E−04, A₁₀ =−4.974E−04, A₁₂ = 6.687E−05, A₁₄ = 5.972E−06, A₁₆ = −5.146E−06 EighthSurface k = 0.000, A₄ = −1.613E−02, A₆ = 1.695E−03, A₈ = 3.172E−05, A₁₀= −2.193E−04, A₁₂ = −4.379E−06, A₁₄ = 9.229E−07, A₁₆ = 1.197E−06 NinthSurface k = 0.000, A₄ = −8.300E−03, A₆ = 1.732E−03, A₈ = 1.033E−04, A₁₀= 1.298E−05, A₁₂ = −2.649E−05, A₁₄ = 1.111E−07, A₁₆ = 2.724E−06 TenthSurface k = 0.000, A₄ = −7.175E−03, A₆ = −1.061E−03, A₈ = −7.978E−05,A₁₀ = 1.302E−06, A₁₂ = 1.010E−07, A₁₄ = 8.469E−07, A₁₆ = −3.287E−07Eleventh Surface k = 0.000, A₄ = −9.529E−03, A₆ = −7.676E−04, A₈ =1.123E−04, A₁₀ = 1.626E−06, A₁₂ = 1.332E−07, A₁₄ = −4.887E−08, A₁₆ =−1.353E−09 Twelfth Surface k = 0.000, A₄ = −1.194E−02, A₆ = −3.519E−04,A₈ = −7.160E−06, A₁₀ = 1.572E−06, A₁₂ = 4.095E−07, A₁₄ = 2.596E−08, A₁₆= −4.119E−09 Thirteenth Surface k = 0.000, A₄ = −1.040E−02, A₆ =4.246E−05, A₈ = 3.007E−06, A₁₀ = −4.262E−07, A₁₂ = 1.925E−08, A₁₄ =1.185E−09, A₁₆ = −1.213E−10 Fourteenth Surface k = 0.000, A₄ =−1.973E−02, A₆ = 1.274E−03, A₈ = −2.276E−05, A₁₀ = −2.640E−07, A₁₂ =1.481E−10, A₁₄ = 5.884E−11, A₁₆ = 1.155E−11 Fifteenth Surface k =−6.301, A₄ = −8.669E−03, A₆ = 4.496E−04, A₈ = −1.287E−05, A₁₀ =1.473E−07, A₁₂ = 1.087E−08, A₁₄ = −5.094E−10, A₁₆ = 6.416E−12 f1 = 6.15mm f2 = −9.46 mm f3 = 12.43 mm f4 = 37.05 mm f5 = −17.92 mm f6 = −119.05mm f7 = −25.39 mm f45 = −32.09 mm f67 = −21.52 mmThe values of the respective conditional expressions are as follows:

D34/f=0.11

f1/f=0.76f2/f1=−1.54f3/f1=2.02f4/f=4.60f7/f=−3.15f45/f=−3.98f45/f67=1.49f4/f5=−2.07

R5 f/R5 r=−14.95

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length in air for the filter 10) is 9.58 mm, and downsizing ofthe imaging lens is attained.

FIG. 14 shows the lateral aberration that corresponds to the imageheight ratio H, and FIG. 15 shows a spherical aberration (mm),astigmatism (mm), and a distortion (%), respectively, of the imaginglens in Numerical Data Example 5. As shown in FIGS. 14 and 15, accordingto the imaging lens of Numerical Data Example 5, the aberrations aresatisfactorily corrected.

Numerical Data Example 6

Basic data are shown below.

f=8.93 mm, Fno=2.8, ω=33.9°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 6.6830.853 1.5346 56.1 (=νd1)  2* −51.133 0.069  3 (Stop) ∞ 0.111  4* 7.8800.299 1.6355 24.0 (=νd2)  5* 3.682 0.070  6* 4.594 0.877 1.5346 56.1(=νd3)  7* −11.902 1.028 (=D34)  8* −3.035 0.655 1.6355 24.0 (=νd4)  9*−2.802 0.030 10* −42.999 (=R5f) 0.298 1.6355 24.0 (=νd5) 11*   14.098(=R5r) 0.331 12* 9.201 1.328 1.5346 56.1 (=νd6) 13* 7.097 0.449 14*12.009 1.771 1.5346 56.1 (=νd7) 15* 4.382 0.440 16 ∞ 0.300 1.5168 64.217 ∞ 1.600 (Image ∞ plane) Aspheric Surface Data First Surface k =0.000, A₄ = −7.782E−03, A₆ = −1.177E−03, A₈ = −1.175E−04, A₁₀ =4.130E−05, A₁₂ = 3.467E−06, A₁₄ = −1.766E−06, A₁₆ = −9.763E−08 SecondSurface k = 0.000, A₄ = 1.010E−02, A₆ = −1.413E−02, A₈ = 5.073E−03, A₁₀= −9.946E−04, A₁₂ = 8.088E−05, A₁₄ = −3.474E−06, A₁₆ = 2.959E−07 FourthSurface k = 0.000, A₄ = 1.775E−02, A₆ = −2.060E−02, A₈ = 7.347E−03, A₁₀= −1.405E−03, A₁₂ = 8.285E−05, A₁₄ = 2.845E−07, A₁₆ = −1.140E−06 FifthSurface k = 0.000, A₄ = 4.923E−03, A₆ = −1.347E−02, A₈ = 3.690E−03, A₁₀= −3.028E−04, A₁₂ = −5.945E−05, A₁₄ = −1.046E−05, A₁₆ = 3.130E−06 SixthSurface k = 0.000, A₄ = 5.430E−03, A₆ = −3.288E−03, A₈ = 1.168E−03, A₁₀= −6.284E−05, A₁₂ = −1.431E−05, A₁₄ = 1.804E−06, A₁₆ = 3.837E−08 SeventhSurface k = 0.000, A₄ = −3.444E−03, A₆ = 3.905E−04, A₈ = 7.971E−04, A₁₀= −4.552E−04, A₁₂ = 8.340E−05, A₁₄ = 1.510E−05, A₁₆ = −4.234E−06 EighthSurface k = 0.000, A₄ = −8.809E−03, A₆ = 1.883E−03, A₈ = 1.021E−04, A₁₀= −2.569E−04, A₁₂ = −2.580E−06, A₁₄ = 1.061E−07, A₁₆ = 2.437E−06 NinthSurface k = 0.000, A₄ = −6.076E−03, A₆ = 1.390E−03, A₈ = −5.220E−05, A₁₀= 1.206E−05, A₁₂ = −3.014E−05, A₁₄ = −1.892E−06, A₁₆ = 1.631E−06 TenthSurface k = 0.000, A₄ = −8.118E−03, A₆ = −9.568E−04, A₈ = −6.600E−07,A₁₀ = 7.759E−06, A₁₂ = 1.983E−07, A₁₄ = 1.370E−06, A₁₆ = 1.286E−07Eleventh Surface k = 0.000, A₄ = −1.040E−02, A₆ = −4.846E−04, A₈ =1.569E−04, A₁₀ = 4.655E−06, A₁₂ = 7.814E−07, A₁₄ = 5.787E−08, A₁₆ =−3.112E−09 Twelfth Surface k = 0.000, A₄ = −1.719E−02, A₆ = 3.869E−04,A₈ = −7.549E−05, A₁₀ = −3.876E−06, A₁₂ = −6.834E−07, A₁₄ = −2.606E−08,A₁₆ = −3.026E−09 Thirteenth Surface k = 0.000, A₄ = −1.312E−02, A₆ =1.113E−04, A₈ = 1.496E−05, A₁₀ = −2.630E−06, A₁₂ = −9.533E−08, A₁₄ =2.912E−09, A₁₆ = 3.249E−10 Fourteenth Surface k = 0.000, A₄ =−2.466E−02, A₆ = 1.435E−03, A₈ = −2.603E−05, A₁₀ = −7.716E−07, A₁₂ =3.384E−09, A₁₄ = 3.450E−10, A₁₆ = 2.218E−10 Fifteenth Surface k =−10.832, A₄ = −8.158E−03, A₆ = 4.589E−04, A₈ = −1.305E−05, A₁₀ =1.129E−07, A₁₂ = 1.019E−08, A₁₄ = −5.212E−10, A₁₆ = 6.303E−12 f1 = 11.11mm f2 = −11.18 mm f3 = 6.32 mm f4 = 27.43 mm f5 = −16.67 mm f6 = −74.40mm f7 = −14.04 mm f45 = −35.47 mm f67 = −11.99 mmThe values of the respective conditional expressions are as follows:

D34/f=0.12

f1/f=1.24f2/f1=−1.01f3/f1=0.57f4/f=3.07f7/f=−1.57f45/f=−3.97f45/f67=2.96f4/f5=−1.65

R5 f/R5 r=−3.05

Accordingly, the imaging lens of Numerical Data Example 6 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length in air for the filter 10) is 10.41 mm, and downsizingof the imaging lens is attained.

FIG. 17 shows the lateral aberration that corresponds to the imageheight ratio H, and FIG. 18 shows a spherical aberration (mm),astigmatism (mm), and a distortion (%), respectively, of the imaginglens in Numerical Data Example 6. As shown in FIGS. 17 and 18, accordingto the imaging lens of Numerical Data Example 6, the aberrations aresatisfactorily corrected.

According to the above-described imaging lens of the embodiment, it isachievable to obtain a wide angle of view (2ω) of 80° or larger. Forreference, the imaging lenses according to Numerical Data Examples 1 to6 have wide angles of view of 64.2° to 85.2°. According to the imaginglens of the embodiment, it is possible to take an image of wider rangethan the range that can be taken by a conventional imaging lens.

Furthermore, in these days, with advancement in digital zoom technologyto enlarge any area of an image obtained through an imaging lens byimage processing, an imaging element having a high pixel count has beenfrequently used in combination with a high-resolution imaging lens. Incase of such imaging element having a high pixel count, alight-receiving area of each pixel decreases, so that an image obtainedby the imaging element tends to be dark. In order to fix this issue,there is a method of improving light sensitivity of the imaging elementusing an electrical circuit. According to the method, however, since anoise component that does not directly contribute to formation of animage is also amplified as the light sensitivity increases, it isnecessary to provide another circuit for reducing the noise. Accordingto the imaging lenses of Numerical Data Examples 1 to 6, Fno is as smallas 2.1 to 2.8. According to the imaging lens of the embodiment, it ispossible to obtain sufficiently bright image without providing suchelectrical circuit.

Accordingly, when the imaging lens of the embodiment is applied in acamera for mounting in a portable device such as cellular phones,portable information terminals, and smartphones, and relativelysmall-sized cameras, such as digital still cameras, security cameras,onboard cameras, and network cameras, it is possible to attain both highfunctionality and downsizing of the cameras.

The disclosure of Japanese Patent Application No. 2014-002821, filed onJan. 10, 2014, is incorporated in the application by reference.

While the invention has been explained with reference to the specificembodiment of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

What is claimed is:
 1. An imaging lens comprising: a first lens havingpositive refractive power; a second lens; a third lens; a fourth lens; afifth lens; a sixth lens; and a seventh lens, arranged in this orderfrom an object side to an image plane side, wherein said first lens,said second lens, said third lens, said fourth lens, said fifth lens,said sixth lens, and said seventh lens are arranged respectively with aspace in between, said fifth lens is formed in a shape so that a surfacethereof on the image plane side has a positive curvature radius, andsaid seventh lens is formed in a shape so that a surface thereof on theimage plane side and a surface thereof on the object side are aspheric.2. The imaging lens according to claim 1, wherein said third lens isdisposed away from the fourth lens by a distance D34 on an optical axisso that the following conditional expression is satisfied:0.05<D34/f<0.2, where f is a focal length of a whole lens system.
 3. Theimaging lens according to claim 1, wherein said first lens has a focallength f1 so that the following conditional expression is satisfied:0.5<f1/f<2.0, where f is a focal length of a whole lens system.
 4. Theimaging lens according to claim 1, wherein said first lens has a focallength f1 and said second lens has a focal length f2 so that thefollowing conditional expression is satisfied:−4<f2/f1<−0.5.
 5. The imaging lens according to claim 1, wherein saidfirst lens has a focal length f1 and said third lens has a focal lengthf3 so that the following conditional expression is satisfied:0.5<f3/f1<4.
 6. The imaging lens according to claim 1, wherein saidfourth lens has a focal length f4 and said fifth lens has a focal lengthf5 so that the following conditional expression is satisfied:−8<f4/f5<−1.5.
 7. The imaging lens according to claim 1, wherein saidfourth lens has a focal length f4 so that the following conditionalexpression is satisfied:2<f4/f<15, where f is a focal length of a whole lens system.
 8. Theimaging lens according to claim 1, wherein said seventh lens has a focallength f7 so that the following conditional expression is satisfied:−8<f7/f<−1, where f is a focal length of a whole lens system.
 9. Theimaging lens according to claim 1, wherein said second lens has anAbbe's number νd2 so that the following conditional expression issatisfied:20<νd2<35.
 10. The imaging lens according to claim 1, wherein said fifthlens has an Abbe's number νd5 so that the following conditionalexpression is satisfied:20<νd5<35.
 11. An imaging lens comprising: a first lens having positiverefractive power; a second lens; a third lens; a fourth lens; a fifthlens; a sixth lens; and a seventh lens, arranged in this order from anobject side to an image plane side, wherein said first lens, said secondlens, said third lens, said fourth lens, said fifth lens, said sixthlens, and said seventh lens are arranged respectively with a space inbetween, said seventh lens is formed in a shape so that a surfacethereof on the image plane side and a surface thereof on the object sideare aspheric, said seventh lens is formed in the shape so that thesurface thereof on the object side has a positive curvature radius, saidfifth lens has an Abbe's number νd5, and said third lens is disposedaway from the fourth lens by a distance D34 on an optical axis so thatthe following conditional expressions are satisfied:20<νd5<35,0.05<D34/f<0.2, where f is a focal length of a whole lens system. 12.The imaging lens according to claim 11, wherein said first lens has afocal length f1 so that the following conditional expression issatisfied:0.5<f1/f<2.0.
 13. The imaging lens according to claim 11, wherein saidfirst lens has a focal length f1 and said second lens has a focal lengthf2 so that the following conditional expression is satisfied:−4<f2/f1<−0.5.
 14. The imaging lens according to claim 11, wherein saidfirst lens has a focal length f1 and said third lens has a focal lengthf3 so that the following conditional expression is satisfied:0.5<f3/f1<4.
 15. The imaging lens according to claim 11, wherein saidfourth lens has a focal length f4 and said fifth lens has a focal lengthf5 so that the following conditional expression is satisfied:−8<f4/f5<−1.5.
 16. The imaging lens according to claim 11, wherein saidfourth lens has a focal length f4 so that the following conditionalexpression is satisfied:2<f4/f<15.
 17. The imaging lens according to claim 11, wherein saidseventh lens has a focal length f7 so that the following conditionalexpression is satisfied:−8<f7/f<−1.
 18. The imaging lens according to claim 11, wherein saidsecond lens has an Abbe's number νd2 so that the following conditionalexpression is satisfied:20<νd2<35.